Method of vulcanizing rubber and resulting products



0 may Patent Nova 5,

HENRY B. MORSE, 0F DANS, MASSACHUSETTS, ASSIGNOB, BY MESNE ASSIGNMENTS,

T0 ALBERT C. BURRAGE,

JRH, OF IPSWICH, MASSACHUSETTS HQETHQD OF 'VULCANIZING RUBBER AND RESULTING ERODUCTS No wing,

This invention relates to the art of-treating rubber or rubber compounds, and has for an object the provision of an improved procedure for the vulcanization of the same in the presence of an accelerator and of compoun or compositions with which to efiect the purpose of the invention.

In the art of rubber manufacture, it has long been known that the vulcanizing process be accelerated by the addition of various compounds in relatively small amounts. The compounds which have been found to thus accelerate vulcanization, known as accelerators, have been constantly added to by research and now include numerous types of substances, both inorganic and organic. Of these substances, the organic compounds are preeminently the more satisfactory and present a wide range of accelerating activity. Those 29 selected for practical use, however, are gentype hereinafter erally restricted to compounds which may be mixed with the rubber or rubber compound without inducing appreciable vulcanizing of feet at atmospheric temperature or during I milling operations, but which actively accelerate the reaction in the customary vulcanizing treatment. Qther accelerator compounds, frequently termed ultra accelerators or semi-ultra accelerators, initiate the vulcanizing reaction sometimes prematurely, either in the cold only or during the mixing operation, resulting in scorching which hinders or entirely prohibits the further use of the rubber or rubber compound. Consequently, such compounds ordinarily have not been used in the manufacture of rubber products, even though they would greatly reduce the time re- 7 quired for vulcanization and may be otherwise suitable lor use in rubber compositions.

By the present invention it is found that the accelerating action of accelerator compounds generally m rubber compositions, may be inhibited (at ordinary and slightly elerated temperatures and during the mixing.

and milling operations) or retarded by the addition of organic compounds of a certain defined, and that thereafter the vulcanizing reaction,--efiectively accelerated by the accelerator,-may be caused to proceed at will by subjecting the rubber com- For example,

Application filed June a, 1929. Serial No. 368,429.

position to be vulcanized to vulcanizing conditions.

It is thought that the accelerator and the inhibitor react or combine .to form a reaction product or compound which does not promote the vulcanizing reaction of the vulcanizable composition (under the preliminary conditions such as mixing and milling) but which,

under the vulcanizing conditions such as increased temperature, dissociates and liberates the accelerator which then acts in its accelerating capacity, and the inhibitor may remain inert or may itself act as an accelerator. In other words, the critical temperture ot the accelerator, with respect to its initiating prematurely the vulcanizing reaction in the rubber, is apparently raised to a point above the temperatures of milling or compounding and within the range ot'the vulcalnizin'g treatment.

lhe compounds manifesting such inhibiting action upon premature initiation of vulcanization by accelerators (and more especially the ultra accelerators and those sometimes referred to as semi-ultra acceleratorsamong which may be mentioned the thiazoles, represented by mercapto benzo thiazole, certain disulfides such as tetra methyl thiuram disulfide, certain monosulfides such as tetra methyl thiuram monosulfide, etc., and their derivatives) are found to typically include the nitroso-amines which may be represented by the empirical formula are alike, they may also contain substituents whichare, difierent or unlike. Thus the substituents lb and R may be aryl radicals and may furthermore be associated with or contain other hydrocarbon radicals or nuclei.-

one substituent may be an unsubstituted aryl group and the other a naphrubber and the usual vulcanizing and filler phenyl-alpha naphthyl nimaterials, together with the desired amounts of the accelerator compound and inhibiting compound, may be compounded and mixed in the usual manner as by milling (without premature vulcanization or scorching), and subsequently molded and vulcanized to the required degree of cure, by heating to the usual range of vulcanization temperatures. lljhe rate of vulcanization and degree of cure obtained may be accurately controlled by the time and temperature of vulcanization, to provide a final cure equal to or better than that obtained without the use of the preliminary inhibiting compound or prehibitors. In a preliminary scorching, test, for em ample, in which the compounds were subjected to especially high temperatures duringthe mixing and milling operations until lscorching was efiected, a rubber composiremoved and again milled on rolls, purposely tion containing:

100 parts rubbertsmoked sheet) 3 parts sulfur 5 parts Znt) part mercapto benzo. thiazole to which .43 parts dibeta naphthyl nitrosoamine was added, was thoroughly milled and mixed on the mixing rolls; the mix was then heated by steam so as to maintain a temperature in the stock of approximately 95 to 100 C.,for 110 minutesv before scorching occurred.

A corresponding stools: without the addition ofdibe'ta naphthylnitroso-amine, upon being milled and mixed, and again milled under like scorched in 65 minutes.

e A similar test carried out upon a rubber compound of the formula:

parts rubber (smoked sheet) parts sulfur parts Zn .75 part dibeta naphthyl nitroso amine 100 parts rubber (smoked sheet) 3 parts sulfur 5 parts ZnO 4 .75 part dibeta naphthyl nitroso-amine was treated in the same way as the preceding compounds and scorching took place conditions of temperature,

.15 part tetra methyl thiuram disulfide .15 part tetra methyl thiuram monosulfide was in 118 minutes, while the same compound, without the dibeta naphthyl nitroso-amine, scorched in about 65 minutes, under the same conditions.

This test, developed for the purpose, serves to measure the degree of the retarding or inhibiting efi'ect of the inhibiting com ound upon the vulcanization reaction and t e accelerating influence or the ultra accelerator at temperatures of about 100 C. or less, as con trasted with vulcanizing temperatures which as ordinarily employed are above 120 G.

Similar tests were carried out employing the same composition, but with a difi'erent lot of smoked sheet rubber which tended to scorch slower (without the addition of ore-- hibitor) than the rubber employed above. The results obtained are given below:

scorching Stock without prehibitor With addition of 0.75 part of:-

' Diphenyl nitroso-amine Dialpha naphthylnitrosoamine-"-4- 62 Phenyl beta naphthylnitroso-amine 93 Phenyl alpha napththylnitroso-amine 93 Diorthotolyl nitroso-amine 97 Phenylorthotolyl nitroso amine 102 Phenylparatolyl nitroso-amine 102 Benzyl phenyl nitroso-amine 52 Methyl'phenyl nitroso-amine.. .-.v.. 5'? Diethyl nitroso-amine 55 Piperidine nitroso-amine 55 Carbazol nitroso-amine 'Ill Same as Formula QI with addition of 1.0 part diphenyl nitroso-amine.

i III Same as FormulaI with addition of .75

' part diphenyl nitros'o-amine.

tie

' manner, care being taken, especially with the compound of Formula I, to prevent preliminary vulcanization of scorching; The mixed compounds were then laid in thin sheets in a -vu1canizing mold and vulcanized at 20 pounds vsteam pressure. Samples of each compound were vulcanized, for periods of 30, 405 and 60 minutes, respectively. One portion of each sample was then subjected to a tensile 110,

strength test, the results being :given in the following table:

' Table I I Care a? twenty pounds steam pressure 30 Minutes ginell IEinal.

1151 e e ongs- 300% 500% lbs. per tion in sq. 1n. percent 'Iv A--- 537 1820 3100 005 45 Minutes iFinali $innl 61151 9. 01123- 300% 560% lbs. per 0511 in sq. in. per cent BQMinutes tgins! final HS] 8 9 01128- 300% 500% lbs. per tion in sq. in. per cent II A.-- 985 2660 4150 550 III A.-- 1135 2380 4175 535 IV 11 1120 2930 4280 025' nitroso-amines, including both like and un-' like substituent groups, and hydrocarbon radicals of both the aliphatic and aromatic series, as indicated in the above list in connection with the scorching test.

The experimental results are presented in I the following tables Table III A B O. D

Smoked sheets 100 100 100 100 Carbon black. 40 40 40 40 Mineral rubber 5 5 5 Zinc oxide 5 5 5 5 Sullur 3 3 3 3 Stearic acid 3 3 3 0, 3 Mercapt ole 0. 8 0. 8 0. 8 0. 8 Phenyl beta naphthyl nitrosoamine 0 0.75 0 0 Beuzyl pheuyl nitroso-amine. 0 0 0.75 0 Carbezo] nitroso-amine 0 0 0 0.75

Cum F01 1 Final 0000 P u d 000% 000% 15: 3:. 32:15:; 7 0 D S .Min pressflm sq. in per cent Table IV A B C D Cure Final. Final Stock P0 d 300% 500% lf gf 322 11H S M111 pressure sq. in. per cent A 20 090 1905 3590 710 B 20 830 2240 4000 700 C 60 20 762 2100 3700 700 D .60 20 667 1905 3200 655 A 20 v 940 2430 4000 675 B 00 20 985 2650 4075 655 C 90 20 985 2600 4000 655 D 90 20 970 2580 4000 655 Table V f A B C D Smoked sheets 100 100 100 100 Carbon black". 40 40 40 40 Mineral rubber. 5 5 5 5 Zinc oxide 5 5 5 5 ultur 3 3 3 3 Steeric acid 3 3 3 3 Mercapto benzo thiazole 0. 8 0.8 0.8 0. 8 DIethyI nitrosorammeu 0 0.75 0 0 Piperidine nitr0so-amine 0 0 0. 75 0 Methyl phenyl ult mo-amine"-.. 0 0 0 0. 75

Cure

Finail inal tensi e e engastock Pounds 300% 500% lbs. per tion in Mm pressure sq. in. per cent 60 20 675 1870 3350 690 60 20 715 1955 3475 675 60 20 820 2200 3780 680 60 20 712 2020 3370 605 7 20 780 2120 3630 050 B. 75 895 2430 3800 055 10 C- 75 20 1055 2820 4220 640 D 75 20 960 2400 3940 055 Table VI A B C D Smoked sheets 100 100 100 100 40 40 40 40 5 5 5 5 5 5 5 5 3 3 3 3 Stearic acid 3 3 3 3 Mercapto benzo thiazole 0v 8 0. 8 0.8 0.8 Dialpha naphthyl nitroso-amine 0 0. 75 0 0 Phenyl tolyl nitroso-amine 0 0 0. 75 0 Ditolyl nitroso-aminc 0 0 0 0.75

Cum Finalrina] tensile e engastock Pounds 300% 500% lbs. per. tion in Min pressure sq. 1n. per cent From the data thus obtained it is to be observed that, not only are the rubber compounds prepared with an addition of the di- 45 phenyl nitroso-amine, for example, free from the tendency toward preliminary vulcanization or scorching, but that when vulcanized at 20 pounds steam pressure and for the periods of time indicated, the vulcanized product ex hibits as good or in some instances a superior cure (with respect to intermediate and final elongation values) than the composition to which such addition has not been made.

It is therefore shown that by means of this 5 invention not only may extremely active accelerators, (which have beenhitherto unavaiL able for use in the rubber industry onaccount of. their very high activity) be safely employed in rubber compounds and mixed and 6 milled without initiating premature vulcanization, but the vulcanized rubber product is initially as good or better than rubber similarly compounded and vulcanized but without the addition of an inhibiting reagent.

It is also indicated that whereas diaryl sub- 1,734.,eee

stituted nitroso-amines are especially efiective, with respect to the prevention of premature acceleration of vulcanization, the alkyl or dialkyl substituted nitroso-amines may also.

N.NO

Carbazole nitroso-amine or nitroso N-carbazole, however, is not strictly in the same category with the other compounds tested and in fact shows but little retarding effect in thescorching test. The piperidine nitroso-amine likewise does not manifest p'ronounced retarding effects. The results are given, however, because they are related to the other nitrosoamine compounds. Their failure to be more effective in these respects may be attributed to the valence linkage between the R and R groups of the nitroso-amine; which will be apparent from the formula of the former compound, as above given.

While the above disclosure relates to a pre ferred procedure, according to the invention, and to specific reagents employed in specific proportions, it is to be understood that variations may be made in both the mode of carrying out the invention and in the nature and amount of the several reagents used, according to the particular conditions of practice and the characteristics desired in the resulting product, as will be clear to those skilled in the art of treating rubber.

This application is a continuation in part of my application, Serial No. 323,556. filed December 3, 1928, and is designated as Case III-4 of a group of continuation applications filed on even date herewith.

I claim:

1. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an organic accelerator characterized by controlling the action of the accelerator with an unlike substituted nitroso-amine containing an aryl and a naphthylsubstituent radical.

2. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an organic accelerator characterized by controlling the action of the accelerator with an unlike substituted nitroso-amine containing a phenyl and a naphthyl substituent radical.

3. Methodof vulcanizing rubber or rubber compositions with a vulcanizing agent and an organic accelerator characterized by controlling the action of the accelerator with phenyl alpha naphthyl nitroso-amine.

IND

1-. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and a sulfur-containing organic accelerator characterized by controlling the action of the accelerator with an unlike substituted 'nitroso-amine containing an aryl and a naphthyl substituent radical.

5. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and a sulfur-containing organic accelerator characterized by controlling the action of the accelerator with an unlike substituted nitroso amine containing a phenyl and a naphthyl substituent radical.

6. Method of vulcanizing rubber or. rubber compositions with a vulcanizing agent and a sulfur-containing organic accelerator characterizedby controlling the action of the accelerator with phenyl alpha naphthyl nitrosoamine. I

7. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an accelerator containing a thiazole nucleus characterized by controlling the action of the accelerator with an unlike substituted nitroso-amine containing an aryl and a naphthyl subs'tituent radical.

8. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an accelerator containing a thiazole nucleus characterized by controlling the action of the accelerator with an unlike substituted nitroso-arnine containing a phenyl and a naphthyl substituent radical.

9. Method of vulcanizing. rubber or rubber compositions with a vulcanizing agent and an accelerator containing a thiazole nucleus characterizedby controlling the action of the accelerator with phenyl alpha naph- 40 thyl nit'rosmamine.

10. Method of vulcanizing rubber or rub ber compositions with a vulcanizing agent and mercaptd benzo thiazole characterized by controlling the action of the accelerator with an unlike substituted nitroso-amine conand mercapto benzo thiazole characterized by controllin' the action of the accelerator with phenyl a pha naphthyl nitroso-amine.

13. accelerator composition comprising an orgi' nic accelerator and an unlike substituted nitroso-amine containing an aryl and a. naphthyl substituent radical...

14. An accelerator composition comprising an organic accelerator and an unlike substituted nitroso-amine containing a phenyl and a naphthyl substituent radical.

15. An accelerator composition comprising an organic accelerator and phenyl alpha naphthyl nitroso-amine.

16.. An accelerator composition comprising a sulfur-containing organic accelerator and an unlike substituted nitroso amine containing an aryl and a naphthyl substituent radica 17. An accelerator composition comprising a sulfur-containingorganic accelerator and an unlike substituted nitroso-amine containing a phenyl and a naphthyl substituent radica I p 18. An accelerator composition comprising a sulfur-containing organic accelerator and phenyl alpha'nap'hthyl nitroso-amine.

19. An accelerator composition comprising an accelerator containing a thiazole nucleus and an unlike substituted nitroso-amine 'con- 22. An accelerator composition compris. ing mercapto benzo thiazole" and an unlike substituted nitrosolamine containing an aryl and a naphthyl substituent radical.

23. An accelerator composition comprising mercapto benzo thiazole and an unlike substituted nitroso-amine containing a phenyl and a naphthyl substituent radical.

24. An accelerator composition comprising mercapto benzo thiazole and phenyl alpha naphthyl nitroso-amine.

Signed by me at Boston, this 1st day of June, 1929.

HENRY B. MORSE.

Massachusetts Hit 

